Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $213.94   4.246%   $223.0239   $223.02   $223.00   $223.00  
  Purchase #2 $165.37   6.871%   $176.7326   $176.73   $176.75   $176.70  
  Purchase #3 $232.40   3.366%   $240.2226   $240.22   $240.20   $240.20  
  Purchase #4 $44.63   7.560%   $48.004   $48.00   $48.00   $48.00  
  Purchase #5 $184.66   6.699%   $197.0304   $197.03   $197.05   $197.00  
  Purchase #6 $170.78   8.715%   $185.6635   $185.66   $185.65   $185.70  
  Purchase #7 $222.83   5.129%   $234.259   $234.26   $234.25   $234.30  
  7 purchase totals = $1,234.61       $1,304.9360   $1,304.92   $1,304.90   $1,304.90